A bicycle frame is known, e.g., from WO 01/15963. In bicycles the chain drive has established itself. Many types of bicycles are equipped with a derailleur or with a hub gearing on the rear wheel. In the case of a derailleur, the design dictates that the components are externally mounted on the frame or the rear-wheel, where they are exposed to dirt, since they are continuously subject to the effects of weather.
The high degree of effectiveness exhibited by a derailleur when new is drastically diminished as a result of dirt, so that a significant portion of the force applied by the driver must be expended to overcome the resistances within the gearing. In the case of a fall, or upon contact with rocks or branches, the components can be damaged or torn from the frame. A hub transmission eliminates these disadvantages.
However, when the gears are integrated into the back wheel hub the weight of the back wheel increases. When the gear is moved to the frame the mass of the back wheel is reduced, which has a beneficial effect, particularly in the case of spring-loaded bicycles, since the driving comfort increases with the reduction of unsprung masses. Particularly in the case of so-called mountain bikes, which are used in the open country, a reduction in the mass of the rear wheel has a noticeable effect.
In rapid downhill travel not only the increased travel comfort but also the increased driving safety is important. If large spring paths are to be realized the drive chain must run over a chain adjuster so that the changing distance between the rotating axis of the back wheel and the rotating axis of the drive pinion can be equalized. In order to forego the use of a chain adjuster the transmission is integrated into the frame in such a way that the rotating axis of the gear output lies close to the center of the rear wheel trajectory.
A bicycle frame into which the gearing has been integrated is very complicated to produce since it is necessary to closely define not only the position of the gearing relative to the rear-wheel wing to be attached to the frame, but also the spacing of the gear from the pedal-bearing axle, by means of which the drive force is introduced. Involved here is a precision part that is produced by hand.
Known from U.S. Pat. No. 4,955,247 is a gear arrangement for a bicycle in which the pedal-bearing shaft and the gear output shaft are mounted in the same housing. The transmission of torque from the pedal-crank to the gear output shaft is performed by bevel gears.